Abstract

I will present low-temperature quantum transport measurements of GaAs cleaved-edge overgrowth wires. The conductance of the lowest wire mode approaches the 2 e2/h at high temperatures but is suppressed strongly

for decreasing temperatures, reaching 1 e2/h at ~ 80 mK, where it remains for T< 80 mK. We have confirmed that the electrons cool to about 10 mK, well below 80 mK. This suggests that the electron spin degeneracy is fully lifted (B= 0), presenting evidence for a strong nuclear spin polarization. Our data are qualitatively consistent with recent theory predicting a spin-selective Peierls transition in the Luttinger liquid regime, presenting experimental evidence for a helical nuclear state.

Further, I will present experimental data and theory for intrinsic charge fluctuations and metastable states in GaAs surface-gate defined double quantum dots in the few electron regime. These charge fluctuations set an intrinsic upper limit for spin-qubit coherence and can be suppressed by reducing temperature and/or tunnel-coupling of the dots to the reservoirs.